1. Field of the Invention
The present invention relates to methods for producing a quaternary ammonium hydroxycarboxylate, a mixture of quaternary ammonium hydroxycarboxylates having different ammonium ions, a quaternary ammonium salt of inorganic acid, and a mixture of quaternary ammonium salts of inorganic acid having different ammonium ions. A quaternary ammonium salt of organic acid has been widely used as a surfactant and is also useful as a raw material for phase transfer catalysts, medicines, and cosmetics. Recently, a highly pure quaternary ammonium salt is demanded in the fields of electronic materials for use as a cleaning agent for electronic parts, a developer of resists, etc. The quaternary ammonium salt is also particularly useful as electrolytes for electric double layer capacitor that has recently come to attract attentions as a battery system for an uninterruptible power supply, a hybrid car, etc. It is known that the cycling characteristics, etc. of electric double layer capacitor are affected by a trace amount of impurities such as water and halogen, and therefore, a quaternary ammonium salt of inorganic acid for use in this field is particularly required to be highly pure.
2. Description of the Prior Art
Alkyl halides and dialkyl sulfates are conventionally known as a quaternizing agent for a tertiary amine. These quaternizing agents are, however, not suitable for use in the manufacture of electronic parts because halogen ion and sulfate ion contaminate the quaternary ammonium salt. Other known quaternizing agents include dialkyl carbonates and organic carboxylic ester. However, these compounds are not industrially suitable because the quaternizing reaction is relatively slow and should be conducted in a polar solvent such as alcohol to prevent the generation of carbon dioxide or carbon monoxide due to the decomposition of dialkyl carbonates and organic carboxylic ester. Thus, no quaternizing agent is known in the art, which enables industrially efficient production of a highly pure quaternary ammonium salt by the quaternization of a tertiary amine in the absence of solvent.
It has been known to produce a quaternary ammonium salt of organic carboxylic acid by the reaction of a quaternary ammonium hydroxide and a carboxylic acid. In another known method, a quaternary ammonium acid sulfate is treated with an alkali hydroxide and a carboxylic acid. However, since the process is complicated, these methods are less practicable for industrial use because of high costs. In addition, the methods fail to produce highly pure products because a small amount of sulfate ion or alkali metal remains in the products.
In still another known method, an quaternary ammonium alkyl carbonate is reacted with an organic carboxylic acid. This method can produce a highly pure quaternary ammonium salt of organic carboxylic acid. However, the process for synthesizing the quaternary ammonium alkyl carbonate from a tertiary amine and a dialkyl carbonate is long, and the method requires a expensive dialkyl carbonate. Therefore, this method is not industrially applicable.
In still another known method, a quaternary ammonium salt of organic carboxylic ester is directly produced by the reaction of a tertiary amine and an organic carboxylic acid. However, the rate of reaction is generally low to require a long reaction time, and the yield of product is not sufficiently high. To solve this problem, is proposed a method for reacting an organic carboxylic ester and a tertiary amine in a polar solvent. For example, Japanese Patent Application Laid-Open No. 62-174036 discloses a method for carrying out the reaction in a polar solvent such as alcohol, amide and nitrile. Japanese Patent Application Laid-Open No. 6-329604 proposes to react an organic carboxylic ester and an tertiary amine in a polar solvent in the presence of a small amount of organic carboxylic acid. However, since the use of the polar solvent and the addition of the organic carboxylic acid are required, these method are not industrially advantageous.
Thus, there has been known no method that is capable of efficiently producing a quaternary ammonium salt of organic carboxylic acid at high yield by the quaternization of a tertiary amine with an organic carboxylic ester in the absence of a polar solvent.
A quaternary ammonium salt of inorganic acid is generally produced by quaternizing a tertiary amine with an alkyl halide to prepare a quaternary ammonium halide that is then converted into a quaternary ammonium salt of inorganic acid by replacing the halide ion with an acid radical of a desired acid. However, this method involves a problem of a portion of the starting halide remaining in the product.
To solve this problem, is known a method of producing a quaternary ammonium salt of inorganic acid by the reaction of an inorganic acid with a quaternary ammonium alkyl carbonate or a quaternary ammonium hydrogencarbonate. Japanese Patent Publication No. 7-116113 discloses a method of producing a quaternary ammonium salt of inorganic acid, which comprises a first step of reacting a tertiary amine with a carbonate ester to obtain a quaternary ammonium carbonate and a second step of converting the quaternary ammonium carbonate to a corresponding quaternary ammonium salt of inorganic acid by mixing with an inorganic acid while removing the generated carbon dioxide gas from the reaction system. This method creates little impurities such as water and halogen. However, according to the working examples thereof, the reaction of triethylamine and dimethyl carbonate of the first step is carried out at a high reaction pressure, 0.5 MPa, for a long reaction time, 12 h. Additionally, the relatively expensive dialkyl carbonate is decomposed to carbon dioxide and alcohol in the second step. Further, if a low-boiling inorganic acid is used to remove the by-produced carbon dioxide from the reaction system, a portion of the inorganic acid is removed together with carbon dioxide.
As mentioned above, the conventionally known methods for producing a quaternary ammonium salt of inorganic acid are carried out at a high pressure for a long reaction time, and have problems of decomposition of the relatively expensive starting dialkyl carbonate into carbon dioxide and alcohol, difficulty of reuse of the starting compound, and easy loss of the starting compound.
A mixture of salts of organic or inorganic acid having different quaternary ammonium ions is generally produced by mixing different quaternary ammonium salts of organic or inorganic acid that are separately produced, or by quaternizing a mixture of starting trialkylamines corresponding to the intended quaternary ammonium salts. These methods, however, require different starting compounds to increase the cost for apparatus and switching operations. In addition, the starting amines having different alkyl groups are generally expensive. Thus, no industrially advantageous method for producing a mixture of salts of organic or inorganic acid having different quaternary ammonium ions is known in the art. As will be described in Comparative Example 1, it was found by the inventors that the relatively expensive dimethyl carbonate was decomposed when the reaction was carried out in the same manner as in the present invention while using dimethyl carbonate that is known as a quaternizing agent, although a mixture of quaternary ammonium salts of organic acid was obtained.
Thus, no industrially advantageous method is known in the art in the production of a mixture of plural salts of organic or inorganic acid having different quaternary ammonium ions from only one starting tertiary amine.
A first object of the present invention is to provide an industrially advantageous method for producing an quaternary ammonium salt of organic acid.
A second object of the present invention is to provide an industrially advantageous method for producing a mixture of salts of organic acid having different quaternary ammonium ions.
A third object of the present invention is to provide an industrially advantageous method for producing a highly pure quaternary ammonium salt of inorganic acid.
A fourth object of the present invention is to provide an industrially advantageous method for producing a mixture of salts of inorganic acid having different quaternary ammonium ions.
As a result of extensive study on the production method of a quaternary ammonium salt of organic acid by the quaternization of a tertiary amine, the inventors have found that a highly pure quaternary ammonium salt of organic acid is produced in industrially advantageous manner by quaternizing a tertiary amine using a specific hydroxycarboxylic ester as a quaternizing agent even in the absence of a polar solvent.
In addition, as a result of extensive study on the production method of a mixture of salts of organic acid having different quaternary ammonium ions, the inventors have surprisingly found that such a mixture is obtained by a trans-alkylation between only one tertiary amine and a specific hydroxycarboxylic ester under selected reaction conditions.
Further, as a result of extensive study on the production method of a quaternary ammonium salt of inorganic acid, the inventors have found that the quaternization of a tertiary amine by a specific hydroxycarboxylic ester proceeds at a sufficient reaction rate in a first step even at a low pressure and without using a solvent, thereby producing the quaternary ammonium salt of organic acid efficiently, and further found that a highly pure quaternary ammonium salt of inorganic acid is obtained by reacting the quaternary ammonium salt of organic acid with an inorganic acid in a second step without the decomposition of a by-produced hydroxycarboxylic acid.
Still further, as a result of extensive study on the production method of a mixture of salts of inorganic acid having different quaternary ammonium ions, the inventors have found that a mixture of quaternary ammonium hydroxycarboxylates having different quaternary ammonium ions is produced from only one tertiary amine and a specific hydroxycarboxylic ester by selecting the reaction conditions of the above first step, and further found that a mixture of corresponding quaternary ammonium salts of inorganic acid is obtained by reacting the mixture with an inorganic acid in a second step without decomposing the by-produced hydroxycarboxylic acid and without changing the proportion of the starting mixture of quaternary ammonium hydroxycarboxylates.
Thus, in a first aspect of the present invention, there is provided a method for producing a quaternary ammonium hydroxycarboxylate, which comprises a step of reacting a tertiary amine represented by the following Formula 2: 
wherein R4, R5 and R6 are the same or different, and each is alkyl, alkenyl or aryl, each optionally having a substituent group, a pair of R4, R5 and R6 being optionally bonded to form an aliphatic or aromatic ring together with nitrogen to which each pair is bonded, or one of R4, R5 and R6 being optionally bonded to the other two to form two-ring structure,
with a hydroxycarboxylic ester represented by the following Formula 1: 
wherein R1 is alkyl, alkenyl, aralkyl or aryl, R2 and R3 are the same or different and each is hydrogen, alkyl, alkenyl, aralkyl or aryl, thereby producing the quaternary ammonium hydroxycarboxylate represented by the following Formula 3: 
wherein R1 to R6 are the same as defined above.
In a second aspect of the present invention, there is provided a method for producing a mixture of quaternary ammonium hydroxycarboxylates, which comprises a step of reacting a tertiary amine represented by the following Formula 2a: 
wherein three R7 groups are the same or different, and each is alkyl, alkenyl or aryl, each optionally having a substituent group, and two of three R7 groups being optionally bonded to form an aliphatic or aromatic ring together with nitrogen to which each R7 is bonded,
with a hydroxycarboxylic ester represented by the following Formula 1xe2x80x2: 
wherein R1 to R3 are the same as defined above, with the proviso that R1 is different from at least one of three R7 groups of Formula 2a, thereby producing a mixture containing at least two quaternary ammonium hydroxycarboxylates represented by the following Formula 3x:
[R74-nN+R1n][R2R3C(OH)COOxe2x88x92]xe2x80x83xe2x80x83(3x)
wherein R1 to R3 and R7 are the same as defined above, and n is an integer from 1 to 4.
In a third aspect of the present invention, there is provided a method for producing a quaternary ammonium salt of inorganic acid, which comprises:
a first step of reacting the tertiary amine 2 with the hydroxycarboxylic ester 1, thereby producing the quaternary ammonium hydroxycarboxylate 3; and
a second step of reacting the quaternary ammonium hydroxycarboxylate 3 produced in the first step with an inorganic acid, thereby producing the quaternary ammonium salt of inorganic acid represented by the following Formula 5: 
wherein R1 and R4 to R6 are the same as defined above, and X is an acid radical of the inorganic acid.
In a fourth aspect of the present invention, there is provided a method for producing a mixture of quaternary ammonium salts of inorganic acid, which comprises:
a first step of reacting the tertiary amine 2a with the hydroxycarboxylic ester 1xe2x80x2, thereby producing a mixture containing at least two quaternary ammonium hydroxycarboxylates 3x; and
a second step of reacting the mixture of quaternary ammonium hydroxycarboxylates with an inorganic acid, thereby producing a mixture containing at least two quaternary ammonium salts of inorganic acid represented by the following Formula 5a:
[R74-nN+R1n]Xxe2x88x92xe2x80x83xe2x80x83(5a)
wherein R1, R7, n and X are the same as defined above.